Hydrogen exchange measurements have been able, in some cases, to distinguish different kinds of protein motions and to provide site-resolved information on their identity, their extent, their equilibrium and kinetic parameters, their response to ambient conditions and mutations, and their relationship to functional properties. As part of the effort to understand the significance of the dynamic dimension of protein structure and its role in protein function, these hydrogen exchange capabilities need to be improved and extended to more proteins. Studies are proposed of staphylococcal nuclease, dihydrofolate reductase, and cytochrome c initially, and other proteins more broadly. To better understand the relationships that connect hydrogen exchange behavior to protein structure and dynamics, a large quantity of results will be used to test and refine theoretical models that attempt to relate protein properties and hydrogen exchange. To extend the scope of native state hydrogen exchange methods, the mode of action of osmolytes, and their use as reverse denaturants, will be pursued. Also, larger proteins, which promise to change the balance between local fluctuations and larger unfolding reactions measured by hydrogen exchange, will be studied. To study the functional role of the dynamic dimension of protein structure, hydrogen exchange approaches will be applied to the study of enzymatic function.